The invention is directed to stiff and impact resistant closures derived from the stiff and impact resistant blends including poly(propylene) or poly(ethylene/propylene) and calcium carbonate; stiff and impact resistant compositions including poly(propylene) or poly(ethylene/propylene) and calcium carbonate; methods for increasing stiffness and impact resistance of a poly(propylene) or poly(ethylene/propylene) resin, or a closure; and a method for measuring the impact strength of a closure or a resin at a reduced temperature. A presently preferred blend contains from about 40 to about 60 weight percent of poly(propylene) or poly(ethylene/propylene) and from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, the treated particles having a particle size of from about 2.5 to about 3.5 microns.
Polymers such as polypropylene or polymers formed from the polymerization of propylene and at least one other monomer have been utilized extensively for making closures. It is desirable to have a stiff and impact resistant closure, both at room temperature, as well as at reduced temperature. Properties of increased stiffness and increased impact resistance are advantageous for any structural materials, to avoid cracking when the structural materials are impacted.
The properties of the closure at reduced temperature are important when closures are to be used on containers stored at reduced temperatures, or when closures are destined to be used on containers for use in cooler climates. Therefore, improvements in closures made from compositions including polypropylene have focused on increasing the stiffness and the impact strength of the polymer. However, when one of these properties is improved, the other is usually worsened. For example, when stiffness is increased, impact strength normally is decreased. It would be very useful to be able to improve both of these characteristics at the same time.
I have now discovered that a conventional filler for polymeric compositions, of a certain particle size and in a certain proportion, may surprisingly provide the highly desirable result of improving both impact strength and stiffness of the polymeric composition to which it is added. This additive is calcium carbonate, used as a filler in polymeric compositions.
Inorganic fillers such as calcium carbonate are frequently added to polymers. Examples of other fillers include talc, kaolin, clays, silica, alumina, mica, carbon black, TiO2, ZnO and Sb2O3. Conventionally, calcium carbonate is utilized as a filler for resins such as polypropylene. When improved impact resistance is desired, other additives to achieve this property are introduced, such as rubber. Therefore, although calcium carbonate has been utilized as an additive to reduce the cost of a resin, it has not been considered to be useful for the improvement of both stiffness and impact resistance of a resin. Moreover, addition of calcium carbonate to a resin has not been considered to improve impact resistance both at room temperature and at reduced temperature.
Therefore, a polymeric composition for use in making closures which has both improved stiffness and improved impact resistance would be desirable.
The invention is directed to a closure for a container comprising a top and a depending shell, said closure is formed of a stiff and impact resistant polymeric blend having from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene); and from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns, wherein said closure has a falling weight impact resistance at xe2x88x9220xc2x0 C. of from about 0.4 to about 2.5 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
The invention is also directed to a closure for a container comprising a top and a depending shell, said closure is formed of a stiff and impact resistant polymeric blend having from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene) and from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns, wherein said closure has a falling weight impact resistance at room temperature of from about 0.8 to about 4.0 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
The invention is also directed to a closure for a container comprising a top and a depending shell, said closure is formed of a stiff and impact resistant polymeric blend having from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene) and from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns, wherein said closure has a falling weight impact resistance at xe2x88x9220xc2x0 C. of from about 0.4 to about 2.5 joules, a falling weight impact resistance at room temperature of from about 0.8 to about 4.0 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
The invention is also directed to a method of increasing stiffness and impact resistance in a closure comprising the steps of:
a) making a stiff and impact resistant polymeric blend by
compounding from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene) with
from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns; and then,
b) molding said blend into a closure.
The invention is also directed to a stiff and impact resistant polymeric composition comprising:
from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene); and,
from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns,
wherein said composition has a falling weight impact resistance at xe2x88x9220xc2x0 C. of from about 0.4 to about 2.5 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
Such a composition is very useful as a structural material for a closure. The invention is also directed to a stiff and impact resistant polymeric composition comprising:
from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene); and,
from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns,
wherein said composition has a falling weight impact resistance at room temperature of from about 0.8 to about 4.0 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
The invention is also directed to a stiff and impact resistant polymeric composition comprising:
from about 40 to about 60 weight percent of a polymer selected from the group consisting of poly(propylene) and poly(ethylene/propylene); and,
from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns,
wherein said composition has a falling weight impact resistance at xe2x88x9220xc2x0 C. of from about 0.4 to about 2.5 joules, an impact resistance at room temperature of from about 0.8 to about 4.0 joules and a stiffness at room temperature of from about 1800 to about 2200 megapascals.
For any of the above-mentioned compositions, the fatty acid may be stearic acid; and the compositions may also include at least one additive such as pigments, lubricants, anti-oxidants, emulsifiers and a combination thereof. The compositions described above may be used to manufacture any product wherein structural materials having increased stiffness and impact resistance is desirable, such as automobile parts, containers, or laundry tubs among others; in addition to the closures described herein.
The invention is also directed to a method for increasing the impact strength and stiffness of a polypropylene or poly(ethylene/propylene) resin comprising the step of
compounding from about 40 to about 60 weight percent of said resin with from about 25 to about 35 weight percent of calcium carbonate particles treated with fatty acid, wherein said calcium carbonate particles have a particle size of from about 2.5 to about 3.5 microns.
The impact strength of the above-mentioned method may be room temperature impact strength, cold temperature impact strength, or room temperature impact strength and cold temperature impact strength.
In the methods described above, the compounding may be carried out in an extruder at a die temperature of 350-425xc2x0 F., a rate of 20-40 lbs/hr and a screw speed of 200-500 rpm to obtain good dispersion of the calcium carbonate particles; and the extruder may be a twin screw extruder having at least a first temperature zone, a second temperature zone, a third temperature zone and a fourth temperature zone. The first, second, third and fourth temperature zones may each be maintained at a temperature of 400xc2x0 F.
The invention is also directed to a method for measuring impact strength of a closure at a reduced temperature comprising the steps of:
a) conditioning a closure for forty hours at 23xc2x0 C. and 50% relative humidity according to ASTM D-4101 to produce a conditioned closure;
b) acclimating said conditioned closure for two hours at a reduced temperature to produce an acclimated closure; and then,
c) measuring impact resistance of said acclimated closure by the falling weight impact test according to ASTM D-5628-94.
The reduced temperature for the method described above may be 0xc2x0 C., xe2x88x9220xc2x0 C. or xe2x88x9240xc2x0 C.